KUOPIO, FINLAND-- Environmental tobacco smoke (ETS) is known to incite acute attacks in children with asthma. But new research indicates that it can also produce more chronic effects. A recent Finnish study has demonstrated that asthmatic children who are exposed to ETS have decreased peak expiratory flow rates (PEFRs), as well as increased respiratory symptoms and greater bronchodilator use.[1] Furthermore, the study by Schwartz et al provides evidence that the effects of ETS on PEFR are dose-dependent.

The study included 74 children with asthma (defined as either physician-diagnosed asthma or chronic wheezing) and 95 with chronic cough. The children, all of whom were between the ages of 7 and 12 years, were identified through a screening questionnaire and studied during the winter and spring of 1994.

The children were asked to measure their PEFR every morning and evening and to note the results in a diary. They were also asked to report respiratory symptoms, daily medication use, and whether someone had smoked inside their home.

EFFECT IN PEFR

The investigators discovered that 11% of the asthmatic children and 14% of the children with cough were exposed to ETS at home. When the asthmatic children exposed to ETS at home were compared with the other asthmatic children, both morning and evening mean PEFRs were found to be about 40 L/min lower in the exposed children. Controlling the analysis for a variety of potentially confounding factors--including age, height, weight, sex, atopic status, socioeconomic status, previous day's temperature and humidity, day of the week, and use of maintenance drugs--had no appreciable effect on the size of the decrease in PEFR.

In the asthmatic children, Schwartz et al also found a strong, negative association between the extent of ETS exposure and PEFR. For example, mean morning PEFR was more than 340 L/min in the asthmatic children with no ETS exposure but less than 290 L/min in those exposed to ETS on more than 10% of the study days.

An association between ETS exposure and decreased PEFR was also found in the children with chronic cough. However, this association was much smaller than that seen in the asthmatic children (it averaged about 12 L/min) and did not reach statistical significance.

EFFECT ON SYMPTOMS

Daily variations in ETS exposure were only weakly associated with daily changes in PEFR in the asthmatic children. However, ETS exposure on a given day strongly predicted the next day's bronchodilator use; in fact, it increased the odds that such medications would be needed by a factor of more than 10. A single day's exposure to ETS only weakly predicted the next day's symptoms (coughing and phlegm production), but two days' ETS exposure increased the odds of coughing by more than 12 and the odds of phlegm production by almost 8.

Because the children with chronic cough only did not use bronchodilators, Schwartz et al could not assess the impact of ETS exposure on medication use in this cohort. Furthermore, because symptoms other than cough were less common in this group than in the asthmatic children, no attempt was made to correlate ETS exposure with symptoms on subsequent days.

IMPLICATIONS OF STUDY RESULTS

The association between ETS exposure and the next day's bronchodilator use in children with asthma is quite suggestive, the investigators believe. If the children in this study increased their use of bronchodilators after acute exposure to ETS, it might blunt the association between acute exposure and alterations in PEFR. That a decrease in PEFR was nonetheless found underscores the harmful effect of ETS on children, the researchers noted.

The weaker association between ETS exposure and PEFR in the children with chronic cough suggests that healthier children are less affected by ETS exposure, the authors suggested. Asthmatic children have also been shown to be more susceptible to the effects of air pollution than are other children.

The study had several limitations; for example, the number of children exposed to ETS was not large. "Parents of asthmatic children tend not to smoke at home--in most cases, the person who smoked was probably a relative or visitor," said lead study author Joel Schwartz, PhD, associate professor of environmental epidemiology, Harvard School of Public Health. However, he added, more children may be exposed to ETS as the prevalence of smoking among women increases.

Another limitation of the study is the fact that it measured only the number of days of ETS exposure, not the amount of exposure per day. Furthermore, the study did not attempt to investigate the possible confounding effects of ETS exposure during pregnancy. However, given that few of the parents of the asthmatic children in this study smoked, the investigators doubt that in utero exposure significantly influenced their findings.

According to Dr. Schwartz, there are two take-home messages from this study. First, "we urge physicians to talk to their patients who smoke about the hazards to their children. A large amount of data suggest that most physicians don't actually discuss smoking with patients--they assume that patients already know smoking is bad." Parents should also be warned about the harmful effects that a houseguest's smoking may have on their children.

Second, current antismoking educational programs for children are inadequate because they often start at the high school level rather than in elementary school, said Dr. Schwartz. Most smokers take their first cigarette between the ages of 8 and 12 years, he noted.

--Linda Pembrook

Reference
1. Schwartz J, Timonen KL, Pekkanen J. Respiratory effects of environmental tobacco smoke in a panel study of asthmatic and symptomatic children. Am J Respir Crit Care Med. 2000;161:802-806.

 

How Long Do the Effects of In Utero Exposure to ETS Last?

LOS ANGELES--A number of studies show that maternal smoking in the perinatal period is linked with decreased pulmonary function in infants. But do the effects last into adolescence? A study of schoolchildren conducted at the University of Southern California says the answer is "yes"--the change in lung function persists.[1] In the study, in utero exposure to maternal smoking was found to be independently associated with decreased lung function in school-age children. Flow rates through the small airways were especially affected. The investigation included 3,357 children in fourth, seventh, and 10th grades. Their parents completed a questionnaire asking about the children's current and past exposure to household environmental tobacco smoke (ETS) and exposure to maternal smoking in utero. The students also underwent lung function tests. The researchers found that 19.3% of the students had been exposed to maternal smoking in utero, and 41.5% had been exposed to household ETS at some point during their lives. The largest percentage deficits in lung function associated with in utero exposure to maternal smoking affected flow in the small airways, as reflected in a 4.6% decrease in mean mid-expiratory flow and a 6.2% drop in forced expiratory flow. In addition, the peak expiratory flow rate was 3.0% lower in the children exposed in utero to maternal smoking. These reductions in flow did not vary significantly with sex, race, grade, income, or parental education. Lung function deficits were also detected in the children exposed to household ETS. However, the percentage changes were much smaller than those associated with in utero exposure. Furthermore, once the analysis was controlled for in utero exposure, the effects of household ETS exposure diminished markedly. "Our study shows that maternal smoking during pregnancy has persistent effects on children's respiratory health, in addition to other adverse effects," said Frank D. Gilliland, MD, PhD, an associate professor of preventive medicine at the University of Southern California's Keck School of Medicine. "We need to increase our efforts to counsel women to quit smoking, especially when they are pregnant." --Linda Pembrook

Reference 1. Gilliland FD, Berhane K, McConnell R, et al. Maternal smoking during pregnancy, environmental tobacco smoke exposure and childhood lung function. Thorax. 2000;55:271-276.